Whether the Environmental Protection Agency (EPA) must quantify a states contribution to downwind non-attainment before adopting a FIP; and whether the EPA's interpretation of "contributes significantly" may permissibly define "significant" interstate pollution to include the cost effective reductions an upwind state can make to improve air pollution in downwind states.

Under the Clean Air Act’s (CAA) “good neighbor” provision, states are responsible for pollutants that cross state lines and “contribute significantly” to pollution in downwind states. The EPA promulgated the Transport Rule to implement the good neighbor provision in 2011, in response to pollution emitted by 28 upwind states that affected downwind states’ ability to meet air quality standards. Multiple state and local governments, as well industry and labor groups challenged the Rule.

The D.C. Circuit held that the Transport Rule exceeded the EPA’s statutory authority. The court concluded that the Transport Rule might require states to reduce emissions by an amount greater than their own contribution to downwind states non-attainment of air quality standards. The court also held that the EPA exceeded its authority under the CAA by setting out its own Federal Implementation Plan (FIP) without first allowing states to achieve the required pollution reductions at the state level.

On review, Petitioners argue that court of appeals lacked jurisdiction because the challengers had failed to timely seek review of the final orders at issue. Petitioners further argue that the CAA does not excuse a state from adopting a state implementation plan if the EPA does not quantify the states individual contribution to downwind non-attainment. Moreover, Petitioners argue, Respondents’ challenge to the EPA’s “significant contribution” analysis was not properly before the court, and in any event the EPA’s interpretation of that statutory phrase was entitled to Chevron deference.

American Lung Association v. EME Homer City Generation was combined with Environmental Protection Agency v. EME Homer City Generation and only deals with the questions presented in that petition.